1. Field of the Invention
The invention relates to a semiconductor integrated circuit (IC) device having a high breakdown voltage for controlling a high current, and to a method of manufacturing the semiconductor integrated circuit device. The semiconductor integrated circuit device according to the invention may be used as an IC for a switching power supply, an IC for driving the power system of an automobile, and an IC for driving a flat panel display. Specifically, the invention relates to a semiconductor integrated circuit device that incorporates a trench lateral power metal-oxide-semiconductor field-effect transistor (MOSFET) and one or more planar semiconductor devices, such as a planar MOSFET and a bipolar transistor, on a semiconductor substrate, and the method of manufacturing the semiconductor integrated circuit device.
2. Description of the Related Art
Recently, portable instruments have been widely used, and intelligent communication technologies have been developed. In association with these movements, power ICs that incorporate power MOSFETs have become very important devices. The conventional power IC combines a discrete power MOSFET and a control and drive circuit. In contrast, the new power IC developed recently integrates lateral power MOSFETs into a control circuit. It is required that the new power IC provide reductions in size, electric power consumption, and manufacturing costs thereof, and improve the reliability thereof. To meet these requirements, research and development of lateral power MOSFETs exhibiting a high breakdown voltage and being based on the CMOS process have been vigorously explored.
Usually, the planar power MOSFETs are manufactured using a process very similar to the process for manufacturing planar devices such as bipolar complementary metal-oxide semiconductors (BiCMOSs). Therefore, it is easy to obtain a one-chip power IC by forming a planar power MOSFET and the other planar semiconductor devices on a semiconductor substrate through the CMOS process. However, the integration density of the planar power MOSFET is not very high and improvement of the channel density of the planar power MOSFET, which reduces the on-resistance, is subject to certain limitations because the expanded drain region of the planar power MOSFET is formed along the substrate surface. Therefore, low efficiency of the power supply results and it becomes necessary to use a radiation fin or a large package with low thermal resistance to realize extremely low on-resistance for the power ICs.
Trench lateral power MOSFETs (TLPMs) have been proposed. For example, the present inventors have proposed TLPMs in xe2x80x9cA High Density Low On-resistance, Trench Lateral Power MOSFET with a Trench Bottom Source Contactxe2x80x9d, International Symposium on Power Semiconductor Devices and iCs (ISPD) Proceedings, pp. 143-146, 2001, and in U.S. Patent Publication 6,316,807B1. The trench lateral power MOSFETs facilitate high integration density. The trench lateral power MOSFETs are more advantageous than the planar power MOSFETs because the on-resistance of the trench lateral power MOSFETs is lower than that of the planar power MOSFETs.
FIG. 14 is a cross-sectional view of the active region of a conventional TLPM, which drives a current as a MOSFET. FIG. 15 is a cross-sectional view of the gate region of the conventional TLPM, which leads the gate electrode to the substrate surface.
FIGS. 14 and 15 illustrate a p-type semiconductor substrate 11, a p-type base region 12, an n-type source region 13, a p-type body region 14, an n-type expanded drain region 15, an n-type drain region 16, a trench 17, a gate oxide film 18, a gate electrode 19, a thick oxide film 20, an interlayer oxide film 21, a contact electrode 22, an oxide film 23, a metal source electrode 24, a metal drain electrode 25, and a metal gate electrode 26.
The TLPM having the structure described above is a discrete device. In other words, neither a power IC that integrates a TLPM and a BiCMOS device constituting a control circuit and a protection circuit on a semiconductor substrate, nor any method of manufacturing such a power IC has been realized yet. According to the prior art, a TLPM and an IC for a control circuit and a protection circuit are mounted on a wiring base plate and connected to one another via wires, for example.
The combined system, which combines a discrete TLPM and an IC for a control and protection circuit, poses problems such as an increase in cost caused by an increase in the number of constituent parts and elements and assembly steps, an increase in system size, and a reduction in reliability, as well as noise caused by the elongated wires for feeding gate signals.
In view of the foregoing, it is an object of the present invention to provide a semiconductor integrated circuit device that integrates a TLPM and one or more planar semiconductor devices on a semiconductor substrate. It is another object of the present invention to provide a method of manufacturing the semiconductor integrated circuit device described above.
According to one aspect of the present invention, a semiconductor integrated circuit device comprises a semiconductor substrate, a planar MOSFET that exhibits a low breakdown voltage, and a trench lateral MOSFET that exhibits a high breakdown voltage. The trench lateral MOSFET comprises a trench formed in the semiconductor substrate. A thick oxide film is formed on an upper half of an inner side wall of the trench. A gate oxide film is formed on a lower half of the inner side wall of the trench. A gate electrode is formed along the side wall of the trench and is formed on the thick oxide film and the gate oxide film. A contact electrode is formed in the trench and is spaced apart from the gate electrode by an interlayer insulation film that is interposed between the contact electrode and the gate electrode. A source region having a first conductivity type is formed in the bottom of the trench and is connected to the contact electrode. A base region having a second conductivity type surrounds the source region. An expanded drain region having the first conductivity type surrounds the thick oxide film from outside the trench. A drain region having the first conductivity type is formed in a surface portion of the semiconductor substrate and surrounds the trench. A metal contact electrode is connected to the contact electrode, and a metal drain electrode is connected to the drain region.
In another aspect of the present invention, a semiconductor integrated circuit device is manufactured by conducting a first trench etching to form a trench in the region of a semiconductor substrate for forming a TLPM. A body region and an expanded drain region are formed around the trench. A thick oxide film is formed only on the inner side wall of the trench. A second trench etching is performed to deepen the trench. A gate oxide film for the TLPM and gate oxide films for the planar MOSFETs are formed simultaneously. A gate electrode for the TLPM and gate electrodes for the planar MOSFETs are also simultaneously formed, as well as a base region for the TLPM and a base region for a planar bipolar transistor. A source region and a drain region of one conductivity type for the TLPM, regions of the one conductivity type for the source and the drain of one of the planar MOSFETs, and regions of the one conductivity type for the emitter and the collector of the planar bipolar transistor are simultaneously formed. Regions of the other conductivity type for the source and the drain of the other one of the planar MOSFETs and a region of the other conductivity type for the base of the planar bipolar transistor are simultaneously formed. A contact electrode is buried in the trench through an interlayer insulation film, and constituent metal electrodes are formed.
The semiconductor integrated circuit device according to a preferred embodiment of the present invention integrates a TLPM and a BiCMOS on the same semiconductor substrate, and is obtained by adding the process of forming a trench to the process of forming a BiCMOS.
These, together with other aspects and advantages that will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.